1. Field of the Invention
The present invention relates generally to a radiotherapy marker, and more particularly, to a marker used in CT and MRI imaging.
2. Background Information
In the medical treatment of lesions or focuses such as tumors and the like in the brains and bodies of patients, radiotherapy is a widely conducted treatment. In radiotherapy, a radioactive beam is irradiated from outside of the patient""s body onto a desired focus. When conducting radiotherapy, it is desirable to minimize the amount of irradiation incident onto normal tissue (cells) while maximizing the amount of radioactive energy irradiated onto concerned focuses or lesions. For this purpose, it is generally necessary to precisely irradiate a low dose radioactive beam onto a focus from multiple directions. In the practice of radiotherapy, it is necessary to first develop a medical treatment plan with respect to irradiation positions, irradiation directions, exposure dose, exposure times and the like. For the purpose of developing such a plan, it is indispensable to map out the size of a concerned focus in the patient""s body and the three-dimensional position thereof in a precise manner.
In such medical treatment plans, at the present time, Computed Tomography (CT) imaging using a radioactive beam is typically carried out to investigate the size and position of a focus. In such imaging, a marker is used so that changes in position of the marker and the focus displayed on laminagram images are read and reconfigured to specify the position, size, topography, and the like, of a concerned focus.
Conventionally, as a CT marker, a metallic wire has been employed based on its X-ray absorption characteristics. While this conventional type of marker appears clearly on CT images, a sharp wire may injure a patient and has thus been considered dangerous. In addition, the conventional wire marker becomes rusted after long term service, and accordingly, has poor durability and high fear of contamination. As a result, use of a metallic wire as a CT marker has been deemed far from satisfactory in the art.
In the development of the above-described medical treatment plans, Magnetic Resonance Imaging (MRI) photography is also widely used. In the case of MRI imaging, results of tomography, also using a marker, are reconfigured in the manner described above to specify the size, position, and the like of a concerned focus.
Generally, in MRI there is not so significant a difference between the proton density of normal tissues and that of focuses, while there is a significant difference between their respective relaxation times. This relaxation time has two factors, i.e., longitudinal relaxation (T1) and transverse relaxation (T2), and T1 and T2 are generally of such a nature as to offset signal strength. Consequently, it is necessary to separately obtain images in which T1 is emphasized (T1-weighted spin-echo images) and images in which T2 is emphasized (T2-weighted spin-echo images).
In the prior art, as a marker for T1-weighted spin-echo images, water solutions of margarine, salad oil, paramagnetic materials and so forth have been employed, while water has been employed as a marker for T2-weighted spin-echo images. The markers must thus be changed prior to respective cases of photographing T1-weighted spin-echo images and T2-weighted spin-echo images, which in turn leads to deteriorated precision in the positioning of a concerned focus, and further makes handling markers and photographing complicated and troublesome. These have been the problems associated with the conventional art in the present field.
To overcome these problems, the present inventors have provided markers wherein paramagnetic material is added uniformly into viscous liquid and gel hydrophilic substances, which has enabled photographing both T1- and T2-weighted spin-echo images. The present invention aims at making them easier to use, and gives them even more excellent durability.
Accordingly, it is an object of the present invention to provide a marker for CT image photographing which is safer and more durable than conventional CT markers and which appears clearly on images based on the preferable absorption thereof.
Another object of the present invention is to provide a marker for CT image photographing, which is safe and durable, and which also outputs high signals in both T1 and T2-weighted spin-echo MRI images and responds to both of them.
It is still another object of the present invention to provide a marker that can be employed for both CT and MRI imaging, which enables one to conduct CT image photographing and MRI (T1, T2) image photographing by use of a single marker.
The present invention has been made on the basis of the knowledge that the present inventors found in their search for a new CT marker to replace the conventional metallic wire, that silicon resin and fluorocarbon resin appeared clearly on CT images.
As a marker for MRI imaging, the inventors also found that elastomer of rubber and so forth, and organogel polyethylene gel and so forth output high signals in response in photographing T1 and T2-weighted spin-echo images, and appear clearly on such images, thereby obtaining an MRI marker having excellent durability.
Still further, a combination of the above CT marker and MRI marker enables the acquisition of clear images in photographing CT as well as T1 and T2 MRI images without mutual image interference. Accordingly, it enables a single marker to be employed in both CT and MRI imaging operations.